Performance & Emission Characteristics of CI Engine Operating on Preheated Oil … doc/2017/IJMIE_OCTOBER2017/IJ… · · 2017-09-30Exhaust gas can be used as the heat ... investigated

International Journal of Management, IT & Engineering Vol. 7 Issue 10, October 2017,

ISSN: 2249-0558 Impact Factor: 7.119

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174 International journal of Management, IT and Engineering

http://www.ijmra.us, Email: [email protected]

Performance & Emission Characteristics of CI

Engine Operating on Preheated Oil of

Jatropha, Mahua and Rice Bran: A Review

Runjun Saikia

Abstract

Depletion of fossil fuels and continuous increment of

petroleum prices have prompted the interest towards the

use of inedible vegetable oils as alternate source of fuel

for diesel engines. Increased viscosity and poor volatility

is a major problem related to the use of straight vegetable

oils (SVOs) which may cause a number of operational

and durability problems. Preheating is a simple technique

to lower the density and viscosity of vegetable oil before

utilizing in an engine for getting better results. Exhaust

gas can be used as the heat source for this purpose. In this

paper, a comprehensive study has been conducted to

review the performance and emission characteristics of a

compression ignition engine fuelled with preheated

Jatropha, Mahua and Rice Bran Oil. Diesel is taken as the

baseline fuel for comparison of performance and emission

characteristics for all the three cases [1]. A single

cylinder, four stoke, constant speed, water cooled, direct

injection diesel engine is used for the experiments. The

acquired data were analyzed for various parameters such

as thermal efficiency, brake specific fuel consumption

(BSFC), smoke opacity, CO 2 , CO and HC emissions.

Keywords:

Diesel Engine;

Jatropha Oil;

Mahua Oil;

Preheated;

Rice Bran Oil.

Lecturer, Department of Mechanical Engineering, Sibsagar Polytechnic, Demow, Assam, India.




1. Introduction

The developing countries like India were adversely impacted by the overexploitation of fossil

fuels and continuing rise in global price of crude oil [2]. Renewable nature and significant

environmental benefit of vegetable oils have keen the interest towards the use of both edible and

non edible vegetable oils as fuel for Diesel engine. Studies involving the use of raw vegetable

oils as a replacement for diesel fuel indicate that a diesel engine can be successfully fuelled with

100% vegetable oil on a short-term basis. However, long-term engine durability studies show

that fuelling diesel engines with 100% vegetable oil causes engine failure due to engine oil

contamination, stuck piston rings, and excessive carbon build-up on internal engine components.

Short-term engine testing indicates that vegetable oils can readily be used as a fuel source when

the vegetable oils are used alone or are blended with diesel fuel [3]. But if greater blend ratio of

the oil and its long-term use is required, modification of the properties of the vegetable oil has to

be done. Preheating of vegetable oil blends is one of the viable solutions of the problem.

Preheating is done to obtain the properties of vegetable oil mainly viscosity and density close to

that of diesel.

2. Literature Review

Explaining Agarwal D. et al. [4] investigated the performance and emission characteristics of a

Diesel engine fuelled with Jatropha oil (preheated and blends). They have found that thermal

efficiency of preheated Jatropha oil was slightly lower than diesel. However, thermal efficiency

for preheated Jatropha oil was higher than unheated Jatropha oil. Unheated Jatropha oil shows

exhaust temperature lower than preheated Jatropha oil but higher than diesel. Heating the

Jatropha oil result in lower smoke opacity compared to unheated oil but it is still higher than

diesel. Preheated Jatropha oil shows marginal increase in CO2 emission compared to diesel.

However, heating the Jatropha oil results in lower CO emission compared to unheated Jatropha

oil at higher loads only. HC emissions are lower at partial load, but tend to increase at higher

loads for all fuels. Diesel fuel operation produced lower HC emissions compared to Jatropha oil.

Pugazhvadivu et al. [5] experimented diesel engine using mahua oil (both unheated and

preheated) as fuel. They have found that the BTE was lowered when it was running with mahua

oil. The maximum BTE using unheated mahua oil was 20% as against 28% with diesel at 75%

load. The maximum BTE of 22.8% was obtained at full load using preheated mahua oil. It is




found that the smoke density of the engine with unheated mahua oil operation was higher than

diesel and with preheating the smoke density was lower than that of diesel. HC emission was

lowered for mahua oil combustion with preheating. The HC emission was 85 ppm with

preheating compared to mahua oil (140 ppm) and diesel (120 ppm) at full load. CO concentration

was higher with mahua oil operation compared to diesel at all loads. The CO concentration

reduced significantly with preheating of mahua oil. It was reduced from 0.4% with mahua oil to

0.36% with preheating mahua oil to 1300C. NOX emission was lowered by about 60% compared

to that of diesel. The NOX concentration at maximum load increased by 13% with mahua oil

preheated to 1300C compared to mahua oil without preheating. However, the NOX emission was

significantly lower with preheated mahua oil compared to diesel at all power outputs.

Pugazhvadivu et al. [6] investigated the performance and exhaust emissions of a diesel engine

using diesel, waste frying oil (without preheating) and waste frying oil (WFO) preheated to two

different inlet temperatures (750C and 135

0C). Using preheated WFO, the BSEC and BTE were

improved. The engine exhaust emissions such as CO and smoke were reduced considerably.

Significant improvement in engine performance and maximum reduction in CO and smoke

emissions were obtained using WFO (1350C) compared to WFO (75

0C). From the experimental

findings, it was concluded that WFO could be used as a diesel fuel substitute by reducing its

viscosity to that of diesel by preheating it to a temperature of 1350C.

Ragu et al. [7] have experimented a DI diesel engine fuelled with preheated Rice Bran Oil at

1580C and its respective biodiesel. They have found that diesel has lower brake specific fuel

consumption (BSFC) and Rice bran oil has a higher BSFC at all load. At full load, as compared

to diesel and Rice bran oil, an increase of 8.9% and a reduction of 1.5% in BSEC with preheated

Rice bran oil were observed. The BTE values for diesel, Rice bran oil, and preheated Rice bran

oil are 29.5%, 26.7%, and 27.1% respectively at full load conditions. At full load conditions, the

EGTs are 3480C, 420

0C, and 405

0C for diesel, Rice bran oil, and preheated Rice bran oil

respectively. NOX values at full load conditions for diesel, Rice bran oil, and preheated Rice bran

oil are 2048, 1853, and 1903 ppm respectively. The HC emissions for diesel, Rice bran oil, and

preheated Rice bran oil are 197, 207, and 189 ppm respectively at full load conditions. At full




load operation, the CO emissions are 0.29%, 0.33%, and 0.26% for diesel, Rice bran oil, and

preheated Rice bran oil respectively.

Chauhan et al. [1] evaluated the suitability of Jatropha curcas oil (unheated and preheated) as an

extended fuel for CI engine. Experimental results show that the engine performance with

unheated Jatropha oil is slightly inferior to the performance with diesel fuel. As fuel inlet

temperature of Jatropha oil increased, viscosity decreased and the engine performance improved.

BTE of the engine was lower and BSEC consumption of the engine was higher when engine was

fuelled with unheated Jatropha oil compared to diesel fuel. However, in case of preheated

Jatropha oil, these parameters were superior to unheated Jatropha oil. NOX from Jatropha oil

during the whole range of experiment were lower than diesel fuel. However, for preheated

Jatropha oil, NOx emissions were increased. CO, HC, CO2 emissions from unheated Jatropha oil

were found higher than diesel fuel during the whole experimental range. With preheated Jatropha

oil, the value of CO, HC and smoke opacity was decreased and CO2 emissions were slightly

increased. Result shows that at 1000C of fuel inlet temperature of Jatropha oil, performance and

emissions were favourable but leakage of lube oil from the engine occurred. Therefore, 800C was

evaluated as the optimal fuel inlet temperature, considering the BTE, BSEC and gaseous

emissions and durability and safe operation of the engine.

Kadu et al. [8] used preheated neat karanja oil in a four stroke, single cylinder diesel engine.

Preheating was done from 300C to 100

0C. They have found that at higher speed there was no

significant difference in BSFC when the engine was operated with preheated and unheated

vegetable oil fuels. In other words, BSFC is not affected due to temperature of fuel at inlet

conditions. The karanja oil fuel produced the same BTE at high speed and low speed of the

engine and slightly deviating in the mid of the speed range studied. The heated fuel showed a

marginal decrease in BTE efficiency as compared to diesel fuel operation. Engine power

increases with speed to a maximum value at an engine speed of 3500 rpm. At speeds more than

3500 rpm the power produced is slightly higher than that of ordinary diesel fuel. This clearly

indicates that at higher engine speed conditions the performance of karanja oil fuel can exceed

that of diesel fuel operation. There was significant increase in NOX emissions when running on




neat karanja oil compared to diesel fuel operation. The overall test results showed that fuel

heating was not beneficial at low speed operation.

Based on the above comprehensive literature study, Preheating can offer significant reduction in

viscosity with improved performance and reduced emissions. Specific energy consumption is

reduced when preheated fuel is used. The most of the emission like CO, HC, and smoke are

reduced when the vegetable oils are preheated compared to the unheated raw vegetable oil

although the level of emissions is slightly higher compared to diesel [9]. But if the fuel is heated

up to a maximum temperature then the emissions is somewhat lower than that of diesel. NOX

emission increases with preheating and in certain cases there may be slight increase in CO2

emission. However, the fuel injection system is made up of parts that are very close fitting, such

as the plunger–barrel assembly. High fuel intake temperature may have adverse effects on these

closefitting parts since diesel engines normally run with fuel supplied at ambient temperature.

Consequently, vegetable oil needs to be heated to a temperature that is high enough to give a low

viscosity similar to diesels, but not so high as to damage the injection system [10]. Moreover, if

heated to very high temperatures, low viscosity of the fuel can result in poor fuel droplet

penetration and poor combustion.

In this review study, experimental results of Agarwal D. et al. [4], Pugazhvadivu et al. [5], and

Ragu et al. [7] have been compared with each other and tried to find out the most feasible

preheated oil which would provide the optimum performance and emission characteristics while

comparing with Diesel fuel. The percentage differences in the optimum performance and

emission results using preheated Jatropha, Mahua and Rice Bran oil with reference to Diesel fuel

are being compared with each other.

3. Experimentation

The experimentation carried out by the Researchers can be divided into three groups: Fuel

characterization, engine performance tests and emission measurements. The fuels (Jatropha

SVO, Mahua SVO, Rice Bran SVO and diesel) were analysed for several physical, chemical and

thermal properties and results are shown in Table.1.




Table 1: Properties of Diesel, Jatropha SVO, Mahua SVO, Rice Bran SVO [19, 18, 21]

Property Diesel Jatropha

SVO

Mahua

SVO

Rice Bran

SVO

Density(kg/m3)

840 ±

1.732 917 ± 1 912

995(at

15°C)

Kinematic viscosity

at 400C(cst)

2.44 ± 0.27 35.98 ± 1.3 38.4 33.92

Cloud point(0C) 3±1 9 ± 1 - -

Pour point(0C) -6±1 4± 1 11 -

Flash point(0C) 71±3 229 ± 4 186 198

Carbon

residue(%,w/w)

0.1 0.8 ± 0.1 0.46 -

Calorific value(kJ/kg) 45343 39071 37082 36000

4. Results & Discussion

In this section, it is explained the results of research and at the same time is given the

comparative review.

4.1 Engine Performance Results

Agarwal D. et al. [4] conducted Engine tests for performance and emissions using unheated

Jatropha oil and preheated Jatropha oil. The baseline data were generated using mineral diesel. A

shell and tube type heat exchanger is designed to preheat the vegetable oil using waste heat of

the exhaust gases. The temperature of the preheated Jatropha oil is controlled within a range of

80–900C, a by-pass valve provided in the exhaust gas line before the heat exchanger.

Pugazhvadivu et al. [5] conducted engine performance and emissions tests with diesel

fuel, mahua oil and mahua oil preheated to 130°C with the help of a manually operated electrical

heating arrangement.




Ragu et al. [7] preheated Rice bran vegetable oil to 158°C to bring its viscosity closer to diesel

by using the heat from the exhaust gas and used as fuel. A heat exchanger is used for preheating.

The comparative results obtained for diesel fuel, preheated Jatropha, preheated Mahua and

preheated Rice Bran oil in terms of engine performance parameters like Brake Thermal

Efficiency (BTE), Brake Specific Energy Consumption (BSEC), and Exhaust Gas Temperature

(EGT) at various loading conditions of the Engine are described in the following subsections.

4.1.1 Brake Thermal Efficiency (BTE)

Brake thermal efficiency of preheated Jatropha oil was found slightly lower than diesel. The

possible reason may be higher fuel viscosity. Higher fuel viscosity results in poor atomization

and larger fuel droplets followed by inadequate mixing of vegetable oil droplets and heated air.

However, thermal efficiency for preheated Jatropha oil was higher than unheated Jatropha oil.

The reason for this behavior may be improved fuel atomization because of reduced fuel viscosity

[4]. The maximum thermal efficiency using Jatropha oil was 30% as against 33% with diesel at

85% load. The maximum thermal efficiency (31%) was obtained at 75% load using preheated

Jatropha oil. As compared to diesel and Jatropha oil, a reduction of 2% and an increase of 1% in

brake thermal efficiency with preheated Jatropha oil were observed. Fig. 1 gives the percentage

change of brake thermal efficiency of diesel, Jatropha oil and preheated Jatropha oil with the

engine load.

Fig. 1: Variation of Brake Thermal Efficiency Fig.2: Variation of Brake Thermal

Efficiency with

With load for different Test Fuels load for Test Fuels




The variation of brake thermal efficiency of the engine using diesel, mahua oil and preheated

mahua oil is shown in Fig. 2. The engine thermal efficiency was lowered when it was running

with mahua oil. The maximum thermal efficiency using mahua oil was 20% as against 28% with

diesel at 75% load. The poor combustion behaviour due to lower volatility and higher molecular

weight caused a decrease in thermal efficiency compared to diesel [5]. Fig. 2 also shows that the

thermal efficiency was improved with preheated mahua oil. The reduction in viscosity of

preheated mahua oil observed better evaporation and mixing with air resulting in more complete

fuel combustion. The maximum thermal efficiency (22.8%) was obtained at full load using

preheated mahua oil. As compared to diesel and mahua oil, a reduction of 5.2 % and an increase

of 2.8 % in brake thermal efficiency with preheated mahua oil were observed.

Fig.3: Variation of Brake Thermal Efficiency with Load for Different Test Fuels

At all loads, the engine with diesel operation showed a higher efficiency than both unheated and

preheated Rice Bran oil. At full load, the brake thermal efficiency values for diesel, Rice bran oil

and preheated Rice bran oil are 29.5 %, 26.7 % and 27.1 % respectively [7]. As compared to

diesel and Rice bran oil, a reduction of 2.4 % and an increase of 0.4 % in brake thermal

efficiency with preheated Rice bran oil were observed. Fig. 3 gives the percentage change of

brake thermal efficiency of diesel, Rice Bran oil and preheated Rice Bran oil with the engine

load.

A comparative result of variation in maximum brake thermal efficiencies of the test fuels is

shown in Fig.4. Out of all other test fuels, Maximum brake thermal efficiency of Preheated




Jatropha Oil is only 2% less than that of corresponding diesel fuel. However, the effect of

preheating is highly seen in case of Mahua oil showing an increase of 2.8% in maximum brake

thermal efficiency in preheated Mahua oil compared to raw or unheated Mahua oil.

33

2829.53031

2022.8

26.727.1

10

14

18

22

26

30

34

Max

. BTE

(%

)

Test Fuels

#REF! DIESEL JO PJO MO PMO RBO PRBO Fig.

4: Variation of maximum brake thermal efficiencies of the test fuels

4.1.2 Brake Specific Fuel Consumption (BSFC)

Diesel fuel operation shows lowest Brake Specific Fuel consumption (BSFC) throughout the

operating range. Higher BSFC was observed when running the engine with Jatropha oil. Lower

calorific value of Jatropha oil leads to increased volumetric fuel consumption in order to

maintain similar energy input to the engine [4]. Fig. 5 gives the percentage change of BSFC of

diesel, Jatropha oil and preheated Jatropha oil with the engine load. At 85% loading condition,

Diesel and Jatropha oil shows its lowest BSFC of 0.25 and 0.305 kg/kWh respectively. Preheated

Jatropha oil shows its lowest BSFC of 0.295 kg/KwH at 75% loading condition. As compared to

diesel and Jatropha oil, an increase of 18 % and a reduction of 3.38 %, in BSFC with preheated

Jatropha oil were observed.

Brake Specific Fuel consumption (BSFC) results are not shown by Pugazhvadivu et al. [5] in

their experimentation. BSFC is reverse of BTE. So, the trend of BSFC for baseline Diesel, Raw

Mahua Oil and Preheated Mahua Oil will be reverse of the trend for BTE shown by the fuels.

Due to the lower heating value, Rice bran vegetable oil has a higher Brake Specific Fuel

consumption (BSFC) as compared to Diesel for all loads. When comparing the BSFC of

preheated Rice bran oil and Rice bran oil without preheated, the former has a lower BSFC as




compared to the later. This is due to the improvement in viscosity that leads to better atomization

in the case of preheated Rice bran oil. Fig. 6 gives the percentage change of BSFC of diesel, Rice

Bran oil and preheated Rice Bran oil with the engine load. At full load, the BSFC values for

diesel, Rice bran oil, and preheated Rice bran oil are 0.291, 0.355 and 0.350 kg/kWh

respectively. As compared to diesel and Rice bran oil, an increase of 20.3 % and a reduction of

1.4 %, in BSFC with preheated Rice bran oil were observed [7].

Fig.5: Variation of BSFC with load for different test fuels Fig.6:

Variation of BSFC with load for different test fuels

A comparative result of variation in minimum BSFC of the test fuels is shown in Fig.7. Out of

preheated Jatropha oil and preheated Rice Bran oil, Minimum BSFC of Preheated Jatropha Oil is

only 18% more than that of corresponding diesel fuel whereas it is 20.3% for that of preheated

Rice Bran oil. The effect of preheating is highly seen in case of Jatropha oil showing a reduction

of 3.38% in minimum brake specific fuel consumption of preheated Jatropha oil compared to

raw or unheated Jatropha oil. Exhaust Gas Temperature results are not shown by Pugazhvadivu

et al. [5] in their experimentation.




0.25

0.2910.305

0.295

0.355 0.35

0.2

0.23

0.26

0.29

0.32

0.35

0.38

Min

. BSF

C (

kg

/ K

wH

)

Test Fuels

DIESEL JO PJO RO PRO

Fig.

7: Variation of minimum Brake Specific Fuel Consumption of the test fuels

4.1.1 Exhaust Gas Temperature (EGT)

Unheated Jatropha oil shows exhaust gas temperature lower than that of preheated Jatropha oil

and diesel throughout all the loading conditions of the engine. On higher loading conditions,

EGT of preheated Jatropha oil is more than that of diesel. At 95% loading condition, Preheated

Jatropha oil, Diesel and Unheated Jatropha oil shows EGT of 3700C, 350

0C and 320

0C

respectively. Fig.8 indicates increase in the exhaust gas temperatures of the preheated Jatropha

oil over other fuels [4]. As compared to Diesel and Jatropha oil, an increase of 5.71% and

15.62% in exhaust gas temperature with preheated Jatropha oil was observed at full load.

Fig.8: Increase in the exhaust gas temperatures Fig.9: Variation of EGT with load for

different

Of the Test fuels Preheated Jatropha oil

Over other fuels




At a given load the Diesel has lower value and Rice bran oil shows a higher value of exhaust gas

temperature. The variation of exhaust gas temperature with load for different test fuels is

depicted in Fig.9. At full load, the exhaust gas temperatures are 348°C, 420°C and 405°C for

diesel, Rice bran oil, and preheated Rice bran oil respectively. This can be due to the fact that the

higher viscosity and poor volatility of Rice bran oil lead to poor mixture formation and hence

diffusion combustion phase is more dominant which prolongs the heat release process. This may

lead to higher exhaust gas temperature. As compared to diesel and Rice bran oil, an increase of

16.4 % and a reduction of 3.6 % in exhaust gas temperature with preheated Rice bran oil were

observed at full load [7].

A comparative result of variation in EGT of the test fuels is shown in Fig.10. Out of preheated

Jatropha oil and preheated Rice Bran oil, an increase of 5.71% in EGT is obtained with preheated

Jatropha oil compared to baseline diesel and an increase of 16.4 % in EGT is obtained with

preheated Rice Bran oil compared to baseline diesel. However, a reduction of 3.6% in EGT is

seen with preheated Rice Bran oil compared to that of unheated Rice Bran oil. In case of

Jatropha oil, no improvement in EGT is seen with preheating.

350 348320

370

420 405

200

250

300

350

400

450

500

EGT

( ᴼ

C )

Test Fuels

DIESEL JO PJO RO PRO

Fig.10: A comparative result of variation in EGT of the test fuels

4.2 Emission Results

4.2.1 CO Emission

At lower loads, CO emissions were nearly similar for Diesel, unheated Jatropha oil and

preheated Jatropha oil. But at higher loads, CO emissions were higher for Jatropha oil compared

to that of diesel as shown in Fig.11. This is possibly a result of poor spray atomization and non-

uniform mixture formation with Jatropha oil. However, heating the Jatropha oil results in lower




CO emission compared to unheated Jatropha oil at higher loads only. Maximum CO emission for

all the three test fuels occurs at 95% loading condition. At 95% load, CO emission for Diesel,

unheated Jatropha oil and preheated Jatropha oil are 9 g/KWh, 40 g/KWh, 26 g/KWh

respectively. As compared to diesel and Jatropha oil, an increase of 65.38 % and a decrease of 35

% in CO emission with preheated Jatropha oil were observed [4].

Fig.11: Variation of CO emission of test fuels Fig.12: Variation of CO emission of test

fuels with with load load

CO concentration was higher with mahua oil operation compared to diesel at all loads. This was

due to the improper mixing of mahua oil with air. Fig.12 shows the variation of CO

concentration at various loads on the engine. It is seen that the CO concentration reduced

significantly with preheating mahua oil. CO concentration was reduced from 0.4% with mahua

oil to 0.36% with preheating mahua oil to 130°C. On full load, CO concentration for Diesel was

0.25%. As compared to diesel and Mahua oil, an increase of 30.55 % and a decrease of 10 % in

CO emission with preheated Mahua oil were observed [5].

Carbon monoxide in diesel engines is formed during the intermediate stages of hydrocarbon fuel

oxidation. Rice bran oil results in higher CO emission as compared to diesel. Fig.13 shows the

variation of CO concentration at various loads on the engine.

At full load, the CO emission with Rice bran oil and diesel are 0.33 % and 0.29 % respectively.

The higher CO may be due to the poor spray characteristics as a result of higher viscosity of Rice

bran oil, some of the fuel droplets will not get burned. When these droplets mix with the hot

gases in the later part of the power stroke and early exhaust stroke, oxidation reaction of the fuel




occurs but do not have enough time to undergo complete combustion. However, the CO emission

with preheated Rice bran oil is lower when

Fig.13: Variation of CO concentration at various loads on the engine.

Compared to diesel at full load. As the fuel temperature increases, the CO emission decreases.

The decrease in CO emission is an outcome of improved oxidation of carbon monoxide to

carbon dioxide. The increase in fuel temperature of preheated oil will result in finer spray and

thus good oxidation occurs. This is the reason for reduced CO with high fuel temperature. At full

load; the carbon monoxide emissions are 0.29 %, 0.33% and 0.26 % for diesel, Rice bran oil and

preheated Rice bran oil respectively. As compared to diesel and Rice bran oil, a reduction of 10.3

% and 21.2 %, relatively in carbon monoxide emission with preheated Rice bran oil were

observed at full load [7].

Out of all other test fuels, at full load, preheated Rice Bran oil shows a reduction of 10.3% in CO

emission as compared to Diesel. However, the effect of preheating is highly seen in case of

Jatropha oil showing a decrease of 35% in CO emission of preheated Jatropha oil compared to

that of raw or unheated Jatropha oil.

4.2.2. HC Emission

Diesel fuel operation produced lower HC emissions compared to Jatropha oil. HC emissions are

lower at partial load, but tend to increase at higher loads for all fuels as shown in Fig.14. This is

due to lack of oxygen resulting from engine operation at higher equivalence ratio. At 95% load,

HC emission of Diesel, unheated Jatropha oil and preheated Jatropha oil are 1.2 g/KWh, 2.4




g/KWh and 1.6 g/KWh respectively. As compared to Diesel and Jatropha oil, an increase of 25

% and a decrease of 33.33 % in HC emission with preheated Jatropha oil were observed [4].

Fig.14: Variation in HC emission at various loads of the Fig.15: Variation in HC emission at

various

Test fuels loads of the Test fuels

It is seen that with Mahua oil operation the HC concentration was higher compared to diesel. It is

seen that the HC emission was higher at all loads with Mahua oil. The poor injection of Mahua

oil and its improper mixing with air during preparation phase resulted in incomplete combustion

and higher HC emission. It is seen that the HC emission was lowered for Mahua oil combustion

with preheating. Preheating caused more complete combustion of Mahua oil. As shown in

Fig.15, the HC emission was 85 ppm with preheating compared to Mahua oil (140 ppm) and

Diesel (120 ppm) at full load. As compared to Diesel and Mahua oil, a decrease of 29.16 % and

39.28 % in HC emission with preheated Mahua oil was observed [5].

From the Fig.16, it can be observed that the HC emission with Rice bran oil is higher when

compared to diesel. Higher density and viscosity of Rice bran oil cause poor mixture formation

which results in partially burned hydrocarbons during combustion process. Hence the

hydrocarbon emissions are higher for Rice bran oil. The HC emission for Rice bran oil decreases

with increase in fuel temperature. The reduction in HC emission at higher fuel temperature is due

to better vaporization, as a result of improved atomization. At full load, the hydrocarbon

emissions for Diesel, Rice Bran oil and preheated Rice Bran oil are 197, 207 and 189 ppm




respectively. As compared to Diesel and Rice bran oil, a reduction of 4.1 % and 8.7 % in

hydrocarbon emissions with preheated Rice Bran oil were observed [7].

Fig.16: Variation in HC emission at various loads of the test fuels

Out of all other test fuels, at full load, preheated Mahua oil shows a reduction of 29.16% in HC

emission as compared to Diesel. The effect of preheating is also highly seen in case of Mahua oil

showing a decrease of 39.28% in HC emission of preheated Mahua oil compared to that of raw

or unheated Mahua oil.

4.2.3. Smoke Opacity/ Smoke Density

Smoke opacity for Jatropha oil operation was greater than that of diesel. Heating the

Jatropha oil result in lower smoke opacity compared to unheated oil but it is still higher than

diesel as shown in Fig.17.At 95% load, smoke opacity of Diesel, Jatropha oil and preheated

Jatropha oil are respectively 19%, 45% and 40%. As compared to diesel and Jatropha oil, an

increase of 21% and a decrease of 5% in smoke opacity with preheated Jatropha oil were

observed [4].




Fig.17: Variation in smoke opacity at various Fig.18: Variation in smoke

opacity at various

loads for test fuels loads for test fuels

The variation of smoke density with engine load is shown in Fig.18. It is found that the smoke

density of the engine with Mahua oil operation was higher than diesel. This negative effect is

mainly due to the high viscosity and poor volatility of Mahua oil compared to diesel. The high

viscosity and poor volatility of Mahua oil caused poor fuel injection and mixing characteristics

and incomplete combustion. Further, the mean diameter fuel droplet was higher for vegetable oil

than diesel. The smoke density was higher at full load and it was 6.4 BSU with Mahua oil

operation and 5.7 BSU with Diesel fuel operation. It is also seen from Fig. 18, that the smoke

density was reduced with preheating. The smoke density was 5.4 BSU with preheated Mahua oil

operation. As compared to Diesel and Mahua oil, a reduction of 5.2 % and 15.6 % in smoke

density with preheated Mahua oil was observed. The reduction in smoke density may be due to

the reduction in viscosity and subsequent improvement in spray and fuel air mixing causing good

combustion. The results show that higher reduction in smoke density was achieved at part and

full load conditions. However, only a marginal reduction was observed at low loads. This may be

due to the dilution effect caused by the presence of excess air available at low loads [5].

The variation of smoke density with load for the test fuels is shown in Fig.19. At full load, the

smoke density is 3.2 Bosch Smoke Units (BSU) with Rice bran oil and 2.9 BSU with diesel.

With Rice bran oil, due to its heavier molecular structure and higher viscosity, atomization

becomes poor and this may lead to a higher smoke emission as compared to diesel. However, the




smoke density decreases with preheated Rice bran oil. The smoke emission is 2.8 BSU with

preheated Rice bran oil, which is lower than that of diesel. With preheated Rice bran oil, lower

smoke level as a result of improved combustion can be achieved due to the reduction in viscosity

and a better fuel air mixing rates. As compared to Diesel and Rice Bran oil, a reduction of 3.4 %

and 12.5 % in smoke density with preheated Rice bran oil were observed [7].

Fig.19: Variation of smoke density with load for the test fuels

Out of preheated Jatropha oil, Preheated Mahua oil and preheated Rice Bran oil, at full load,

preheated Mahua oil shows a reduction of 5.2% in smoke density as compared to Diesel. The

effect of preheating is also highly seen in case of Mahua oil showing a decrease of 15.6% in

smoke density of preheated Mahua oil compared to that of raw or unheated Mahua oil.

5. Conclusion

It can be concluded from the above-summarized studies that use of preheated vegetable oil is a

better option than unheated raw vegetable oil in compression ignition engine. Preheating brings

the performance and emission characteristics of a diesel engine close to that of an engine run by

mineral diesel. The review conclusively establishes that maximum brake thermal efficiency

(BTE) of Jatropha Oil preheated to 800C to 90

0C is only 2% less than that of corresponding

diesel fuel. However, the effect of preheating is highly seen in case of Mahua oil preheated to

1300C, showing an increase of 2.8% in maximum brake thermal efficiency compared to raw or

unheated Mahua oil. Maximum brake thermal efficiency of preheated Rice Bran oil is 2.4% less

than Diesel whereas it is 5.2% less than diesel in case of preheated Mahua oil. Out of preheated

Jatropha oil and preheated Rice Bran oil, Minimum BSFC of Preheated Jatropha Oil is only 18%




more than that of corresponding diesel fuel whereas it is 20.3% for that of preheated Rice Bran

oil. The effect of preheating is highly seen in case of Jatropha oil showing a reduction of 3.38%

in minimum brake specific fuel consumption of preheated Jatropha oil compared to raw or

unheated Jatropha oil. Out of preheated Jatropha oil and preheated Rice Bran oil, an increase of

5.71% in EGT is obtained with preheated Jatropha oil compared to baseline diesel and an

increase of 16.4 % in EGT is obtained with preheated Rice Bran oil compared to baseline diesel.

However, effect of preheating is highly seen in Rice Bran oil showing a reduction of 3.6% in

EGT compared to that of unheated Rice Bran oil. In case of Jatropha oil, no improvement in

EGT is seen with preheating. Out of all other test fuels, at full load, preheated Rice Bran oil

shows a reduction of 10.3% in CO emission as compared to Diesel. However, the effect of

preheating is highly seen in case of Jatropha oil showing a decrease of 35% in CO emission of

preheated Jatropha oil compared to that of raw or unheated Jatropha oil. Carbon monoxide

emission of both preheated Jatropha oil and Mahua oil are more than Diesel. Out of all other test

fuels, at full load, preheated Mahua oil shows a reduction of 29.16% in HC emission as

compared to Diesel. The effect of preheating is also highly seen in case of Mahua oil showing a

decrease of 39.28% in HC emission of preheated Mahua oil compared to that of raw or unheated

Mahua oil. Preheated Rice Bran oil shows a reduction of 4.1% in HC emission compared to

Diesel. Hydrocarbon emission of preheated Jatropha oil is more than Diesel. Out of preheated

Jatropha oil, Preheated Mahua oil and preheated Rice Bran oil, at full load, preheated Mahua oil

shows a reduction of 5.2% in smoke density as compared to Diesel. The effect of preheating is

also highly seen in case of Mahua oil showing a decrease of 15.6% in smoke density of

preheated Mahua oil compared to that of raw or unheated Mahua oil. Preheated Rice Bran oil

shows a decrease of 3.4% in smoke density compared to diesel, whereas preheated Jatropha oil

shows an increase of 21% in smoke density compared to Diesel. Considering both performance

and emission results shown by preheated Jatropha oil , preheated Mahua oil and preheated Rice

Bran oil, Rice Bran oil preheated to a temperature of 1580C is considered to be the most

efficient fuel which is comparable to that of Diesel and it is followed by preheated Mahua oil at

1300C and preheated Rice Bran oil at 80-90

0C.




References

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